1. Field of the Invention
The present invention relates to a poppet valve actuator apparatus for opening and/or closing valves of various types, and more particularly, to a valve actuator which is powered or controlled by any suitable means, such as pneumatic or hydraulic fluids, electrical power or by manual operation. While the invention is particularly suitable for use with and is described in connection with a tapered plug type of poppet valve formed of "Teflon" plastic material, the valve actuator of the present invention may also be utilized with a wide variety of valves of different types.
2. Description of the Prior Art
Various types of actuators have heretofore been employed for tapered plug valves formed of "Teflon" plastic material. In general these actuators have been of the so-called impact type and do not provide a consistent closing force that is needed to insure a predictable progressive penetration and leak-tight closure of the tapered plug against the seat over the useful life of the valve. Impact actuators operate on the principle of the application of stored spring energy (usually with a normally closed valve) and pneumatic energy (usually with a normally open valve), through conversion to kinetic energy and force recovery through an anticipated deceleration rate. With these impact units pneumatic venting/pressurization rates, and piston and stem seal friction, often varying with wear, and lubrication, temperature and seal differential pressure cannot be controlled sufficiently to insure acceptable performance. Deceleration forces vary with plug alignment during seating and the depth of plug penetration into the seat. Contamination and temperature variation of the valve material further influence the final force value of seating and closing and vary widely. Impact actuators also suffer from a so-called "first cycle stick" problem wherein sliding devices (especially seals) tend to stick after being maintained in a fixed position for a long period of time.
Patents which are generally pertinent to the present invention are the Stouder U.S. Pat. No. 2,752,930, the Snyder U.S. Pat. Nos. 4,074,688 and 4,073,466, the Goehring U.S. Pat. No. 2,564,569, the Mueller U.S. Pat. No. 3,593,958 and the Weber U.S. Pat. No. 983,101.